Sure, when I first visit a new area it's a great place to scope out local rides. And when I want to share ride routes with friends or see how long or how many hills there are on a potential route I'll plot out what I'm thinking about in MapMyRide first to see what it looks like.
I use it too but only once a month when i record the duration of my monthly workouts into it, mainly for the graph function it gives you, you can then compare month to month or year to year. When im planning a bike tour i use it in conjunction with google earth.
I use it every day for all of my rides and I love it. I'm a stat junkie and I like having the numbers logged for me. It's improved quite a bit in that I think it's a bit more accurate than before too. There's been times when it has logged me as having MPH up to 70! I wish!!! Now, it seems to log me much more reasonable.
I don't really have anything to compare it to though.... I've looked at ridewithgps and if I wasn't using Mapmyride, I'd use that one, but I haven't yet.